Cultivation of plant virus

CULTIVATION OF PLANT VIRUSES

Plant viruses are responsible for causing many diseases of economically important crops, such as tomatoes (tomato spotted wilt virus), corn and sugarcane (wound tumor virus), potatoes (potato yellow dwarf virus), and lettuce (lettuce necrotic yellows). The outcomes of viral infection on some plants are studied here. Same as bacterial and animal viruses, it is essential for microbiologists to be able to cultivate and research plant viruses in a controlled laboratory environment.

Plant viruses could be cultivated by inoculating a plant within a virus suspension by a hypodermic needle or via scratching plant leaves with virus particle . Scratching is aided with an abrasive such as carborundum. This can tend tothe formation of local lesions as well as generally infected plants. For example, a single hair cell of an infected tobacco plant may harbor over 107 (10 million) tobacco mosaic virions. Indeed, as much as the percent of the dry weight of infected leaves may be tobacco mosaic virus.

Transference of infection from cell to cell occurs by entering of virions through bridges that join the cells of plant tissue. Also, in most plant diseases, infected cells can tend to manufacture virus without either disintegrating or lysing. Diseased plant part can be crushed to release plant juices that have the virions, which can then be purified, sometimes to crystals. Using this method in the 1930s, Wendell M. Stanley found purified tobacco mosaic virus in crystal form, the first crystallization of any virus. He was awarded the 1946 Noble Prize in chemistry for the purpose.

In recent years some improvement has been made in the preparation of plant cells which have had their walls removed. Such wall-less cells are bounded only by the cytoplasmic membrane and are called protoplasts. For example, protoplasts obtained from specific tobacco plant cells can be infected directly with tobacco mosaic virus. Progress has also been discovered in the development of monolayer cultures of susceptible cells from the insects that transmit some viral plant diseases. For example, Rhabdovirus has been cultivated in leafhopper cell culture, with a yield of more than 10,000 virions per cell.

“VIRUSLIKE” INFECTIONS AGENTS

During the study of plant and animal diseases, virologists have found some unusual infectious agents called viroids and prions that have some attributes of viruses. However, the structure of those particles differs totally from that of viruses.

Viroids

Viroids are the smallest found infectious agents,that are shown to occur only in plants, they cause several essential diseases of cultivated plants, including potato spindle tuber, citrus exports, chrysanthemum stunt, and cucumber pale fruit. Different from viruses, viroids do not process a protein coat. Some virions are composed up of circular single-stranded RNA; others are linear-stranded RNA molecules. Each contains between 270 and 380 nucleotides. In spite of their small size, viroids replicate in the cell of susceptible plant species, but so far they have not been shown capable of coding for any protein of their own. They appear to be totally dependent on their hosts’ metabolic machinery for replication.

It is found how viroids cause disease. Their location in the nucleus, along with their inability to act as mRNA, proves that they cause host symptoms by direct interference with host gene regulation.

Comparison of nucleic acid sequences has proved that viroids share many detailed structural similarities with a certain region of small nuclear RNAs which are associated with the splicing of introns in animal cells. This finding shows that viroids originated from introns; their pathogenicity might be due to interference with the normal splicing of introns in the body.

Prions

Many transmissible diseases have a slow, progressive course, mostly with a fatal outcome. They are characterized as chronic central nerves system diseases. Incubation periods, from infection to appearances of symptoms, are measured in years, then hours or day! They are caused by peculiar transmissible agents whose characters and behavior suggest an unconventional virus. An example of their unusual character is a high resistance to ultraviolet radiation and heat. These agents are called prions (proteinaceous infectious particles), because they tend to have no nucleic acids at all, with protein their only detectable component. However, like viruses, they reproduce inside cells. It may be proved that prion proteins are coded for by a gene found in normal host DNA.

There are many classic diseases caused by prions, all of them neurological diseases. These include kuru and Creutzfeldt-Jakob disease of humans, and scrapie, a disease of sheep. It has been showed by some researchers that Alzheimer’s disease, the most normal type of senile dementia and an outstanding cause of death among the elderly, mighty also be caused by prions.

VIRUSES AND CANCER

Cancer is the collection name for the number of dreaded diseases characterized by uncontrolled growth of cells within the body. These malignant cells develop from several types of normal tissue cells. The human body harbors more than 100 different kinds of cells, each of which can malfunction in its own distinctive way to cause cancer. More than 100 clinically different type of cancer are recognized, each with a unique set of symptoms. Many of them can be grouped into four major categories.

1. Leukemias: Conditions in which abnormal numbers of white cells (leucocytes) are produced by the bone marrow.
2. Lymphomas: Conditions in which abnormal numbers of lymphocytes ( a type of leucocyte) are produced by the spleen and lymph nodes.
3. Sarcomas: Solid tumors that grow from connective tissue, cartilage, bone, muscle, and fat.
4. Carcinomas: Solid tumors that grow from epithelial tissues and are the most common form of cancer. Epithelial tissues are the internal and external body surface coverings and their derivatives, and thus include skin, glands, nerves, breasts, and the linings of the respiratory, gastrointestinal, urinary, and genital systems.